Micro-step driving for a stepping motor is a driving control method for reducing torque fluctuations during rotation of the motor by stepwise changing current values to be applied to respective phases of the stepping motor so that the current wave form approximates a sine wave. By reducing torque fluctuations, a stepping motor can be driven to rotate evenly with low vibration. However, when a stepping motor includes a permanent magnet thereinside, torque fluctuations while the motor is driven to rotate sometimes cannot be reduced even if the micro-step driving is employed, owing to the influence of holding torque (“detent torque” hereinafter) generated when the stepping motor is not excited.
In a conventional micro-step driving apparatus for a stepping motor, a method described below is employed in order to eliminate the influence of the detent torque. That is, before using a stepping motor, the stepping motor is preliminarily driven and, during the preliminary driving, differences between target rotational angles and actual response rotational angles are measured by a position sensor such as an encoder. Corrective current values necessary for eliminating the differences during the passage of time are calculated and the calculated corrective current values are stored in a storage medium in advance. When the stepping motor is actually used, the corrective current values stored in the storage medium are read out as the time passes from the driving start point of the stepping motor, and the stepping motor is driven to rotate by adding the read out corrective current values to fundamental current values for the micro-step driving (for example, see Patent Document 1).